Rough idle, very poor fuel mileage. - 1995 Chevrolet Blazer

Maybe oxygen sensor.

if the car is loud/noisy there is a hole in the exhaust system and this will cause a rough idle because of a loss of back pressure and the vales will not open and close properly resulting in the rough idle it also will make the engine run hotter and this will cause your spark plug gaps to increase and the spark will be less than needed to ignite the fuel in the cylinder for proper combustion which will result in poor gas mileage and lack of power is the check engine light on?

Sorry guys i was late with my feedback... So here it goes.. I have no check engine light.... Currently running the stock tune as well.. The car has no tps, pcv or egr valve.. It is all controlled by the electronic throttle body which i recently cleaned but didnt help with my problem. I ordered a new fuel pump as well, just didnt get the chance to install it yet. Cant change the fuel filter as it is builtin within the pump. However, shouldnt the fuel pump or fuel filter cause engine stalling, bucking and hesitation? I doubted the fuel pump could be causing this since the problem only occurs at idle. By the way, there is no missing on any of the cylinders.

tune up,fuel filter,air filter,

Hello jack_mathews,

Yes, an o2 sensor tells the computer if the exhaust gases or too rich or too lean. If the computer is told the by the o2 sensor that it's too lean the computer will increase the amount of fuel delivered to the engine thereby reducing your fuel economy, and if the o2 sensor is stuck on lean the computer will continue the increased fuel delivery.

The increased fuel can foul the plugs and cause a rough idle.

Regards,
netvan

check the lambdasensor , can got bad ,and then it gets to much fuel

if your exhaust system is not up to factory spec this will cause idle and rough running conditions,as well as the poor fuel economy, this is due to the sensors not getting accurate readings and sending skewed info to the onboard computer, (the exhaust system has as many as 3 sensors, although i think yours has only one, if you can also remove the catylitic converter, you will get more power./better fuel economy

Sounds like your automatic choke is giving you problems. Check to make sure the choke is operating correctly. If it ins not backing off as the engine gets to operating temp it will cause a rich condition and excessive black smoke out the tailpipe and extremely poor fuel mileage.

Put a new fuel filter on and see if that helps, if it don't, better get a fuel pressure test.

how many miles are on the jeep? there are 2 temp sensors one at the water neck and one at the back of the motor one feeds the computer and may be bad or unplugged and usually will not show a code